In the case of a known reamer of this type (German Patent Application No. 1 427 182) it is considered a shortcoming that the flat reversible cutting bit extending with its plane substantially radially to the body of revolution fails under heavy stresses to introduce the force occurring during the reaming process into the body of revolution with sufficient reliability. There exits then the danger of scoring. The reversible cutting bit adjoins with one wide-side contact surface the radial supporting surface of the body of revolution and projects above its external circumferential surface. Since the bending strength of the reversible cutting bit in the direction vertically to its surface plane is relatively low, it can be expected that in the case of a frictional stress the brittle reversible cutting bit may fracture.
The reversible cutting bit is secured in the recess of the body of revolution by way of a clamping shoe. This clamping shoe is tightened by a screw. The clamping shoe then presses against a wide-side surface of the reversible cutting bit. The fastening of the reversible cutting bit to the body of revolution is, therefore, time-consuming. Another shortcoming is due to the fact that the clamping shoe disposed in front of the reversible cutting bit requires a considerable amount of space in the recess of the body of revolution. The free chip space in the body of revolution ahead of the reversible cutting bit is, therefore, correspondingly smaller. As a result, working with this known reamer is made more difficult.
It is also considered a disadvantage that the narrow-side contact surface of the reversible cutting bit near the longitudinal axis of the body of revolution is supported by two piston-like adjusting bodies. As a result, only a two-point contact is provided which because of the small area is subject to a high stress. In addition, the accurate setting of the reversible cutting bit is exceedingly difficult and inconvenient because during the adjusting both the clamping shoe with its screw and the adjusting bodies with the associated threaded bolt act jointly and interfere with the accurate alignment of the reversible cutting bit. In this case, basically the following operations have to be carried out: Loosening of the adjusting screws, retracting the clamping shoe, insertion of the cutting bit, tightening the clamping shoe with the differential screw, moving the adjusting elements up to the cutting bit by adjusting screws, measuring the diameter of the reamer (micrometer), adjusting the desired dimension by turning the adjusting screws with the clamping shoe tightened. If during this procedure the reaming diameter has been set too large, the whole process has to be repeated. On the whole, therefore, the known reamer is expensive to manufacture and has a complicated structure as a result of which particularly the accurate alignment of the reversible cutting bit is made difficult and the latter is during actual reaming operations subjected to vibratory stresses with the danger of fracture at the point of mounting in the body of revolution.